Okay, I bought and installed a used set of the Depo Euro lights on the SD almost 2 years ago. Love the look but more importantly they perform so much better than US spec lights IMHO. Anyway Driving home the other evening just after dusk it seemed a bulb was out. The high beams and fogs all work but the passenger side low beam was out. I checked the fuse box and cleaned the contacts for that lights fuse ( I will still replace since it is the aluminum type) and still no light. I pulled the bulb and it looks okay not burnt and the filaments look okay ( I need a magnifying glass to make sure ) Anyway I could not find them for sale here on Pelican any thoughts on where to buy ? Also since I do not have all my shop manuals ( in storage ) available does the high beam use a different relay ? Meaning should I check the low beam relay ? Also the P/N # etc on around the ring of the bulb base is really worn / faded and hard to read at all.
I think I can make out "OSRAM" ( sylvania ) but not the wattage. I believe it says 55/65 ( one bulb for high and low ) Thoughts ? I do not want to buy a pricey bulb if not necessary. I do have a pair of bulbs for the uninstalled euro lights for my 500E but again in storage.

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92 500E Silver 66k
82 Porsche 911SC 84K
68 Cadillac ( Gone Now )
03 Suburban Z71 200K
85 300SD 217k From Original Owner ( Dad )

Unless modified after the fact, the headlamps are not powered through relays.

No mods I just did not look too far after I pulled the bulb out. Shame though the High beam worked fine. I need to look again though unless some knows the answer. On these dual filament bulbs do both low and high beam come on when you power the high beams ? If so would an issue in the multi function control stalk possibly case the problem ? I need to replace that as well since the turn signal stalk stopped returning to the center automatically about a year ago.

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92 500E Silver 66k
82 Porsche 911SC 84K
68 Cadillac ( Gone Now )
03 Suburban Z71 200K
85 300SD 217k From Original Owner ( Dad )

Given that the filaments are intact, a common cause for one failing to light in W126s is a corroded or broken slipon terminal that forms the connection with the spade on the bulb. As a check of bulbs, swap left to right.

It looked to me like the high beams only power the high beams and the low beams only power the low beams.

Thanks for the info. And for the idea. I am off tomorrow and will swap the bulbs and or see if I can find my electrical tool box and put a circuit tester on it.
Not having much luck with finding a replacement bulb yet. I know they are available.

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92 500E Silver 66k
82 Porsche 911SC 84K
68 Cadillac ( Gone Now )
03 Suburban Z71 200K
85 300SD 217k From Original Owner ( Dad )

Okay so the bulbs are not hard to find. The ones that kept popping up for me were bulb and lenses. So after I swap the bulb in the a.m. I may bite the bullet and buy a set of the sylvania Ultra's. I have been using these in my 03 Suburban for almost 5 years and love them. Yes the durability comes into play , I think they have been lasting about 2-3 years before one or the other goes out.

__________________
92 500E Silver 66k
82 Porsche 911SC 84K
68 Cadillac ( Gone Now )
03 Suburban Z71 200K
85 300SD 217k From Original Owner ( Dad )